During our functional test, we found the serious defects with I/O function fail.The defects were found with the same Trace code “3BA4TCT”. We tried to swap with different trace code"3BA5SPT",and proceeded the test.There’re 8 pcs PCBAs were re-mounted with different trace code IC, and the test results all showed pass.
We also took the different trace code unites to proceed X-ray for compare, and found the inner layout had difference. 
WHY IT WOULD HAPPEN?
